This invention relates to operator driven fire doors and, more particularly, to a release mechanism for uncoupling the operator from the door.
This invention is particularly concerned with rolling fire doors wherein, under normal conditions in the absence of a fire emergency, the door is coupled to an operator so that it can be selectively opened and closed during the course of a day. Some installations utilize a motor driven operator while other installations utilize a hand driven crank operator having internal gearing. Typically, the operator has an output shaft which is coupled to the rolling fire door shaft by a chain running over two sprocket wheels, each of which is associated with a respective one of the shafts. Alternatively, the operator shaft may be coupled to the door shaft by the direct engagement of gears. Upon the sensing of a fire condition, the door is typically uncoupled from the operator to allow it to close as urged by the force of gravity and the release of stored mechanical energy.
Three types of release mechanisms for such uncoupling are currently in widespread use. The first type is for use with the chain/sprocket wheel arrangement and comprises a finger release device wherein tension applied by a holding chain, conventionally having a fuse link along its length, is transferred to a pair of fingers which effect the meshing engagement of two sets of gear teeth. One of the sets of gear teeth is connected to one of the sprocket wheels and the other set of gear teeth is connected to the shaft associated with that sprocket wheel. Upon release of the tension by the chain, the fingers are allowed to drop so that the gear teeth disengage, thereby separating the sprocket wheel from its associated shaft and uncoupling the motor operator from the door. This arrangement has a number of disadvantages. For example, when the fingers drop they can cause damage by becoming entangled in the operator chain. Further, it is very difficult to set the fingers so that the gear teeth engage.
Another commonly used device for the chain/sprocket wheel arrangement is known as a quartzoid release device which has a built in fusible pellet. Such a device is described in U.S. Pat. No. 3,613,765. This device also has the disadvantage that when the fusible pellet melts, its associated links drop away and can cause damage. Another disadvantage is the high cost of such a device. A still further disadvantage is that this device is only sensitive to fire in its immediate vicinity and cannot be triggered remotely.
When the shafts are coupled by the direct engagement of gears, release is effected by the use of drop-out arms which disengage the gears. Disadvantages of such an arrangement include the requirement that non-lubricated gears be used, as well as its relatively high cost.
It is therefore an object of the present invention to provide a fire door release mechanism which overcomes the disadvantages of the known prior art devices.